Recently, services such as an SNS including sharing images and videos and a VOD whose prices are continuously decreasing as well as a portable information terminal and an STB which support the services are in widespread use. In order to ensure sufficient communication capability for these services and terminals, a demand for widening transmission capability of the optical communication network for supporting the internet has been increasing.
Among the optical communication network, short- and medium-range optical networks that make transmission between cities and the like in relatively short distances are used for transmission within a data center, and therefore, the demand for widening capability is extremely high. A digital coherent optical communication system of a wide dynamic range had been mainly introduced as optical communication of an ultralong distance due to the system's high dispersion resistance, broad dynamic range, and the like. However, along with downsizing of optical components and reduction of prices, application of the system in a shorter distance has been recently examined. Particularly, since the use of silicon photonics technique enables significant downsizing and integration of optical transmitters and optical receivers, the system is expected to considerably contribute to the cost reduction of the optical components in such a relatively closer distance.
Conventionally, as a digital coherent optical receiver used for this digital coherent optical communication system, an optical receiver shown in FIG. 1 as specified in OIF (Optical Internetworking Forum) has been used. FIG. 1 is an extract from FIG. 1 of the following Non Patent Literature 1.